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191.
X. Zhao Y. Itoh Y. Aoyagi T. Sugano K. Hirata Y. Kobayashi T. Ohdaira R. Suzuki T. Mikado 《Journal of Radioanalytical and Nuclear Chemistry》1996,211(1):31-38
Positron and positronium annihilation investigations were applied to nanocrystalline silicon (nc-Si) thin films, for the first time. The nc-Si thin films with average grain diameters of 3–5 nm show intense blue luminescence at room temperature. The nanometer-sized Si crystallites formed in amorphous Si (a-Si) matrix give rise to this luminescence. Very highS-parameters up to 0.62 were observed in the as-grown a-Si thin film suggesting positronium formation in the a-Si layer. The average lifetime of the positrons in the a-Si was determined to be about 520 ps. TheS-parameters dropped significantly to 0.53 by crystallization of the thin film at 800 °C for 10 seconds, which was almost the same to the value observed in bulk Si (100) substrate. Further crystallization from 60 seconds to 1 hour showed smaller change in theS-parameters than that from the a-Si to 10 seconds. The large change in theS-parameters due to the annealing might be caused by the formation of Si nanocrystallites in a-Si matrix suggesting that positron is a sensitive probe for structural investigations of the nc-Si materials. 相似文献
192.
Shiro Kobayashi Hiroshi Uyama 《Journal of polymer science. Part A, Polymer chemistry》2002,40(2):192-209
Topics concerning the cationic ring‐opening polymerization of cyclic imino ethers and functional material production based on the resulting polymers are reviewed. Cyclic imino ethers are readily subjected to isomerization polymerization via cationic initiators. Mechanistic studies have provided a new concept, electrophilic polymerization. Double isomerization polymerization and no‐catalyst alternating copolymerization are interesting examples that show characteristics of the ring opening of cyclic imino ethers. The living polymerization of these monomers affords precisely controlled polymeric materials. Through the use of the unique properties of the product polymers, various functional polymeric materials, such as polymeric nonionic surfactants, compatibilizers, hydrogels, stabilizers for dispersion polymerization, biocatalyst modifiers, and supramolecular assemblies, have been developed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 192–209, 2002 相似文献
193.
Kenshu Fujiwara Masanori Kobayashi Fuyuki Yamamoto Yu-ichi Aki Mariko Kawamura Daisuke Awakura Seiji Amano Azusa Okano Akio Murai Hidetoshi Kawai Takanori Suzuki 《Tetrahedron letters》2005,46(30):5067-5069
The common left-half [C31-C33(OC1-C7)-C40] part of pectenotoxins has been synthesized convergently from the C31-C35, C36-C40, and C1-C7 parts. The C31-C35 part, prepared via a new route shorter than our previous route, was coupled with the C36-C40 part through reductive lithiation and addition reactions to give an adduct stereoselectively, which was converted to a cyclic acetal corresponding to the C31-C40 part. The left-half was synthesized by a three-step process including esterification of the C31-C40 part with the C1-C7 part. 相似文献
194.
Ikehata J Shinomiya K Kobayashi K Ohshima H Kitanaka S Ito Y 《Journal of chromatography. A》2004,1025(2):169-175
The effect of Coriolis force on the counter-current chromatographic separation was studied using centrifugal partition chromatography (CPC) with four different two-phase solvent systems including n-hexane-acetonitrile (ACN); tert-butyl methyl ether (MtBE)-aqueous 0.1% trifluoroacetic acid (TFA) (1:1); MtBE-ACN-aqueous 0.1% TFA (2:2:3); and 12.5% (w/w) polyethylene glycol (PEG) 1000-12.5% (w/w) dibasic potassium phosphate. Each separation was performed by eluting either the upper phase in the ascending mode or the lower phase in the descending mode, each in clockwise (CW) and counterclockwise column rotation. Better partition efficiencies were attained by the CW rotation in both mobile phases in all the two-phase solvent systems examined. The mathematical analysis also revealed the Coriolis force works favorably under the CW column rotation for both mobile phases. The overall results demonstrated that the Coriolis force produces substantial effects on CPC separation in both organic-aqueous and aqueous-aqueous two-phase systems. 相似文献
195.
Yoshiro Kobayashi Takeo Taguchi Tsutomu Morikawa Toyohiko Takase Hiroshi Takanashi 《Tetrahedron letters》1980,21(11):1047-1050
Syntheses of gem-difluorocyclopropyl ketones (3a–d) and their reactions with nucleophiles are described. Ring opening reactions of 3a,c and d with a methanolate and a thiolate anion took entirely different courses of bond scission of the cyclopropane ring. 相似文献
196.
Kakehi A Suga H Kako T Fujii T Tanaka N Kobayashi T 《Chemical & pharmaceutical bulletin》2003,51(11):1246-1252
Some thieno[3,4-b]indolizine derivatives having a 1-naphthylmethylthio, 2-methyl-1-naphthylmethylthio, 2-naphthylmethylthio, or 9-anthrylmethylthio group at the 3-position were prepared and their intramolecular arene-arene interactions were investigated. In comparison with 3-(methylthio)thieno[3,4-b]indolizines which have no such interactions, the (1)H-NMR spectra of title compounds showed large high-field shifts (delta 0.06-0.89 ppm) for the protons of the pyridine ring in the thieno[3,4-b]indolizine, and these values were considerably larger than those (delta <0.3 ppm) in 3-(benzylthio)thieno[3,4-b]indolizines. The UV spectra also exhibited a characteristic absorption band near 425 nm attributable to the arene-arene interaction. In the X-ray analyses of some compounds, however, the presence of both the gauche and the anti conformers at the sulfide spacer were confirmed. 相似文献
197.
Miwa H Makarova EA Ishii K Luk'yanets EA Kobayashi N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(5):1082-1090
Metal-free tetraazachlorin (TAC), -bacteriochlorin (TAB), and -isobacteriochlorin (TAiB) were characterized by electronic absorption, magnetic circular dichroism (MCD), fluorescence, and time-resolved ESR (TR-ESR) spectroscopy, and by cyclic voltammetry. The results are compared with those of metal-free tetraazaporphyrin (TAP). The potential difference DeltaE between the first oxidation and reduction couples decreases in the order TAP>TAiB>TAC>TAB. The splitting of both the Q and Soret bands decreases in the order TAB>TAC>TAP>TAiB. Corresponding to the split absorption bands, MCD spectra show a minus-to-plus pattern with increasing energy in both the Q and Soret regions, which suggests that the energy difference between the HOMO and second HOMO is larger than that between the LUMO and second LUMO. These spectroscopic properties and redox potentials were reproduced by molecular orbital calculations using the ZINDO/S Hamiltonian. The fluorescence quantum yields of the reduced species are much smaller than that of TAP. The zero-field splitting (ZFS) parameters D and E of the excited triplet states (T1) of these species decrease and increase, respectively, on going from TAP to TAC and further to TAB. The D and E values of TAiB are larger than those of the other species. The results are supported by the absence of interaction between the spin over reduced pyrrole moieties of the HOMO and over the LUMO, and by calculations of ZFS under a half-point-charge approximation. 相似文献
198.
Summary The cross-linkings of the surface polymer layer on mono disperse, poly(maleic anhydride-styrene)-modified silica particles
by the reaction with diisocyanate were studied. The extent of cross-linking was estimated by the weight decrease by immersing
the particles in the buffer solution of pH 2.0, 4.0 and 9.0 at a room temperature for 24 h. The reaction of the polymer-modified
silica with 1,6-diisocyanatohexane afforded relatively stable composite particles which lost less than 5 wt% of the polymer
in aqueous solution in the pH range 2.0–9.0. The diisocyanate was a preferable cross-linker to 2,4-diisocyanatotoluene in
terms of stability in acidic or basic aqueous solution. The flexibility of the cross-linker molecule possibly plays an important
role in the cross-linking reaction. The carboxyl and amino groups were formed by treating the cross-linked composite particles
with diluted HCl solution; 5–6 and 0.5–1.1 μmol g-1, respectively. The cross-linked composite particles exhibited the characteristic property of ζ-potential, −44 to −47 mV and
−102 to −107 mV in a neutral aqueous solution and ethanol, respectively.
Received: 26 May 1997 Accepted: 4 August 1997 相似文献
199.
Kobayashi K Ishii K Sakamoto S Shirasaka T Yamaguchi K 《Journal of the American Chemical Society》2003,125(35):10615-10624
The guest- or solvent-induced assembly of a tetracarboxyl-cavitand 1 and a tetra(3-pyridyl)-cavitand 2 into a heterodimeric capsule 1.2 in a rim-to-rim fashion via four intermolecular CO(2)H.N hydrogen bonds has been investigated both in solution and in the solid state. In the (1)H NMR study, a 1:1 mixture of1a and 2a (R = (CH(2))(6)CH(3)) in CDCl(3) gave a mixture of various complicated aggregates, whereas this mixture in CDCl(2)CDCl(2) or p-xylene-d(10) exclusively produced the heterodimeric capsule 1a.2a. It was found that an appropriate 1,4-disubstituted-benzene is a suitable guest for inducing the exclusive formation of 1a.2a in CDCl(3). The ability of a guest to induce the formation of guest-encapsulating heterodimeric capsule, guest@(1a.2a), increased in the order p-ethyltoluene < 1-ethyl-4-methoxybenzene < or = 1-ethyl-4-iodobenzene < or = 1,4-dibromobenzene < 1-iodo-4-methoxybenzene < or= 1,4-dimethoxybenzene < or = 1,4-diiodobenzene. The (1)H NMR study revealed that a CH-halogen interaction between the inner protons of the methylene-bridge rims (-O-H(out)CH(in)-O-) of the 1a and 2a units and the halogen atoms of 1,4-dihalobenzenes and a CH-pi interaction between the methoxy protons of 1,4-dimethoxybenzene and the aromatic cavities of the 1a and 2a units play important roles in the formation of 1,4-dihalobenzene@(1a.2a) and 1,4-dimethoxybenzene@(1a.2a), respectively. A preliminary single-crystal X-ray diffraction analysis of guest@(1b.2b) (R = (CH(2))(2)Ph; guest = 1-iodo-4-methoxybenzene or p-xylene) confirmed that the guest encapsulated in 1b.2b is oriented with the long axis of the guest along the long axis of 1b.2b and that the iodo and the methoxy groups of the encapsulated 1-iodo-4-methoxybenzene are specifically oriented with respect to the cavities of the 2b and 1b units, respectively. 相似文献
200.
Sadahito Aoshima Hiroshi Oda Eiichi Kobayashi 《Journal of polymer science. Part A, Polymer chemistry》1992,30(11):2407-2413
Living cationic polymerization of alkoxyethyl vinyl ether [CH2?CHOCH2CH2OR; R: CH3 (MOVE), C2H5 (EOVE)] and related vinyl ethers with oxyethylene units in the pendant was achieved by 1-(isobutoxy)ethyl acetate ( 1 )/Et1.5AlCl1.5 initiating system in the presence of an added base (ethyl acetate or THF) in toluene at 0°C. The polymers had a very narrow molecular weight distribution (M?w/M?n = 1.1–1.2) and the M?n proportionally increased with the progress of the polymerization reaction. On the other hand, the polymerization by 1 /EtAlCl2 initiating system in the presence of ethyl acetate, which produces living polymer of isobutyl vinyl ether, yielded the nonliving polymer. When an aqueous solution of the polymers thus obtained was heated, the phase separation phenomenon was clearly observed in each polymer at a definite critical temperature (Tps). For example, Tps was 70°C for poly(MOVE), and 20°C for poly(EOVE) (1 wt % aqueous solution, M?n ~ 2 × 104). The phase separation for each case was quite sensitive (ΔTps = 0.3–0.5°C) and reversible on heating and cooling. The Tps or ΔTps was clearly dependent not only on the structure of polymer side chains (oxyethylene chain length and ω-alkyl group), but also on the molecular weight (M?n = 5 × 103-7 × 104) and its distribution. © 1992 John Wiley & Sons, Inc. 相似文献